As the proud owner of a vintage Griffin and George decade resistance box, and in my quest to teach myself some basic electronics, what do the letters mean please? G could be ground? but L and B?
the resistance metered between the top L and the top B coresponds directly to the sum of the removed short plugs. so it will be useful to me, and I can see how it works, but i wondered why two of each G B and L.
also not sure if something is missing from the front plug things? - what are they for? cant find any documentation on line.

The white lines show the connections between G,B, and L and the rest of the circuit (like a circuit diagram).
It does appear that you may be missing a couple plugs at the bottom.
I assume that a plug in those holes completes the connection through the hole.

"In fact this device is configured as a Wheatstone bridge, with terminals and key switches for a battery (B) and galvanometer (G). An unknown resistance can be clamped between the heavy clamp connectors provided with silver contacts and the bridge balanced with an equal resistance of unshorted coils between 0.1 and 50 000 W."